I have a pump gas 518 C.I. motor now, it was a 512 to start with( I changed the crankshaft from a 4.25 stroke to a 4.300 stroke to raise the compression from 9.25 to to 10.29 t0 1
I had switch the heads from a set of ported 906 to a set of MCH CNC ported Eddy RPM that flow almost the same as yours. I use a Comp Cams solid roller that is 260 @ .050 on the intake with .420 lobe lift and 266 @ .050 on the exhaust side with .409 lobe lift, 1.65 rocker ratio. The motor had a stock type low deck six pak on the Eddy heads, it would pull like gangbuster to 7600+ RPM in 1st and 2nd and cross the finish line at 6000 to 6200 RPM. It made peak HP on the engine dyno at 5600 RPM and peak torque at 4500 RPM
I have switch the heads again to a set of Indy SR with M.W. ports and a Indy 400-2 intake with a single Holley 850 DP, it still pulls real hard above 7000 RPM, I have tried shifting it at 6000 RPM before but it runs the fastest shifting it higher
BTW, I have ran 30 inch tall tires with 3.73 gears to 4.30 gears, the car ran the same
best 60 ft. so far is in the 1.41 range on a good track in good weather
Go try it and see what it likes, it will talk to you
Write down somethings to try, change one thing at a time
and have fun